The present invention relates to an intraluminal graft for use in treatment of aneurysms or occlusive diseases.
It is known to use stents and intraluminal grafts of various designs for the treatment of aneurysms such as aortal aneurysms and for the treatment of occlusive diseases such as the occlusion of blood vessels or like ducts such as the bile duct and the ureter (which are all hereinafter called xe2x80x9cvesselsxe2x80x9d). It is known to form such an intraluminal graft of a sleeve in which is disposed a plurality of self expanding wire stents (see Balko A. et al., xe2x80x9cTransfemoral Placement of Intraluminal Polyurethane Prosthesis for Abdominal Aortic Aneurysmsxe2x80x9d, Journal of Surgical Research 40, 305-309 (1986); Mirich D. et al, xe2x80x9cPercutaneously Placed Endovascular Grafts for Aortic Aneurysms: Feasibility Studyxe2x80x9d Radiology, Vol. 170, No. 3, part 2, 1033-1037 (1989)). Such intraluminal grafts are inserted through the femoral artery into the aorta in a catheter. Upon the release of the graft from the catheter it expands to the size of the aorta above and below the aneurysms and bridges the aneurysms.
There are a number of problems associated with such known grafts. These include the problem of twisting or kinking of the graft when it has to extend along a non-linear path which, twisting or kinking can lead to occlusion of the lumen of the graft; lack of precise control of the expansion of the graft in the lumen; avoidance of inadvertent separation of a supporting stent and the covering sleeve; and maintaining the graft against longitudinal movement along the lumen in which it is placed. The present invention is directed to an alternative form of intraluminal graft which provides an alternative to the known grafts.
In a first aspect the present invention consists in an intraluminal graft comprising a tubular graft body which is circumferentially reinforced along its length by a plurality of separate, spaced-apart, maleable wires, each of which has a generally closed sinusoidal or zig-zag shape, one of the wires being located adjacent to one end of the graft body such that alternate crests or apices of the wire projects beyond at least part of that end.
In another aspect the invention relates to a method for positioning an intraluminal graft as defined above comprising introducing a catheter into a vein, artery or other vessel in the body, causing an intraluminal graft as defined above to be carried through the catheter on an inflatable balloon until the graft extends into the vessel from the proximal end of the catheter, inflating the balloon to cause the alternate crests or apices of the one wire to be urged into contact with the wall of the vessel, deflating the balloon and withdrawing the balloon and the catheter from the vessel.
In preferred embodiments of the invention each end of the graft will be provided with a wire which has alternate crests or apices extending beyond the adjacent end of the graft body. While the graft will normally have wires at each end of the graft with their crests extending beyond the graft body it may be necessary or desirable for a surgeon to shorten a graft and this may be achieved by cutting off part of the graft body. In this case the graft will have extending crests at only one end.
The projection of alternate crests or apices of the end wire or wires beyond at least part of the end or ends of the graft body is an important feature of this invention. As the graft is expanded by a balloon the expansion of the wires, and of the balloon, will be limited by the diameter of the tubular graft body except in the region of the alternate crests or apices of the end wire or wires. The balloon will be able to expand these crests slightly more than the remainder of the wire so that they bell outwardly away from the adjacent end of the graft body. The crests are forced into contact with the wall of the vessel and thereby become at least partly embedded into the vessel wall. This belling out of the crests of the wires at one or both ends of the graft body into contact with the inside surface of the vessel wall and then being at least partly embedded in the wall will assist in resisting any tendency for the graft to move longitudinally within the vessel after insertion. The wire crests may extend across the lumen of a vessel opening into the vessel in which the graft is being placed without occluding that lumen. This allows the intraluminal graft to be used in situations in which the aneurysm to be bridged commences closely adjacent divergent blood vessels. In most cases there will be crests of wire actually projecting totally beyond the end of the graft materials. It would, however, be possible to have flaps of graft material protruding up the outside of each crest even though intermediate the crests the end of the graft stops well short of the crests. In this latter arrangement the crests are still free to bell outwardly as has been described above even though the crests do not extend absolutely beyond the end of the graft.
It is preferred that the one wire has a greater amplitude than at least the next adjacent one or two wires. This allows the wires at the end of the graft to be positioned more closely together than would be the case if they were all of the same amplitude. It is desirable to space the wires adjacent the end of the graft that will be placed xe2x80x9cupstreamxe2x80x9d in the patient as close together as is possible as the neck of the aneurysm with which the graft is engaged can be quite short. Close spacing of the wires maximises the number of wires reinforcing that part of the graft in contact with the neck of the aneurysm. The spacing of the rest of the wires is desirably greater than those adjacent the one end of the graft as this avoids unnecessarily reducing the flexibility of the graft.
The wavelength of the wires in the graft is preferably substantially the same when compressed however when expanded the end wires will have a shorter wavelength than the intermediate wires as the intermediate wires will not bear against the arterial wall and may therefore be more fully expanded.
It is preferred that the edge of the one end of the graft is scooped out or scalloped between each projecting crest of the one wire. This reduces the possibility that a piece of the graft between those crests could project into the arterial lumen and partially occlude it or direct blood around the outside of the graft.
The tubular graft body is preferably formed of a thin biocompatible material such as Dacron or PTFE. The tube material is preferably crimped along its length to increase its flexibility, however, uncrimped material may be used in suitable circumstances. In preferred embodiments of the invention the graft body may be formed from a material having a limited amount of diametric elasticity to ensure that it can be expanded into contact with the vessel wall. The length and diameter of the graft body will be determined by the individual circumstances of the application to which the intraluminal graft is to be put. Typically, the vessel will be assessed by X-ray or other similar examination and a suitably dimensioned graft selected for that application.
The wires are preferably formed of stainless steel or another metal or a plastic which is maleable and is biocompatible. Each wire is preferably woven into the fabric of the graft body to integrate the body and the reinforcing wires. This prevents any possibility of the wire reinforcement separating from the graft body during introduction of the graft or throughout its life. If the graft body is of a woven material the wires may be interwoven with the graft body during its production or alternatively they may be interwoven with the graft body after its manufacture. If the graft body is not woven but is knitted or of an impervious sheet material then the wires may be threaded through suitable holes formed in the graft body. The interweaving of the wires with the graft body has been found to be particularly desirable as it prevents separation of the wires from the graft body which could have serious adverse consequences. It has also been found that this technique is very good for causing the graft to expand effectively with the wires.
In alternative embodiments the wires may be held in place by sutures or adhesives or may be sandwiched between layers of a multi-layered tubular graft body. In all of the foregoing arrangements the wires are preferably disposed substantially within the graft body. It is, however, within the ambit of the invention that the wires may be connected to, and be disposed on, the outside surface of the graft body.
The intraluminal grafts according to this invention may be used to treat aneurysms or occlusive disease. In addition to treating aortic aneurysms they are particularly suitable for treating aneurysms of the femoral artery, the popliteal artery, the thoracic segment of the aorta, visceral arteries such as the renal and mesenteric arteries, the iliac artery and the sub-clavian artery. The presence of the metal wires in the intraluminal grafts according to this invention assists in placing the graft as the wires are X-ray detectable. As the wires are arrayed along the length of the graft the complete position of the graft in the body can be continuously monitored.
The grafts according to this invention are typically substantially of constant diameter along their length ie, they are substantially cylindrical. It is possible, however, for the grafts to be frusto-conical in shape with a diameter that increases, or decreases, along the length of the graft.
The ends of the wires are joined together to form a tail which is preferably on the outside of the graft body and is positioned to lie along its radially outer surface. The ends may be joined by welding, by being twisted together or in any other suitable manner. The ends of the wires may inadvertently perforate the vessel in which the graft is placed, however, any such perforation will be occluded by the graft body thus ensuring that such a perforation will not adversely affect the patient. The ends of adjacent wires are preferably spaced apart radially about the graft body so as not to affect its flexibility and to avoid a line of ends engaging the wall of the vessel. The ends of adjacent wires preferably project in opposite directions along the vessel body. When the intraluminal graft is inserted into a vessel those wire ends which engage the inside surface of the vessel wall will assist in preventing the graft from inadvertent movement along the vessel. Causing the ends of alternate wires to project in opposite longitudinal directions along the graft body will assist in preventing longitudinal movement of the graft along the vessel in either direction.
In some circumstances it is desirable to insert two or more overlapped intraluminal grafts according to the present invention. In this case the first or upstream graft preferably has at its downstream end a xe2x80x9cskirtxe2x80x9d without reinforcing wires. This skirt is typically 10 to 15 mm in length. The second or downstream graft is inserted into the downstream end of the first graft and is expanded to engage with it. There is preferably an overlap of at least 10 mm however the degree of overlap is often adjusted so that the downstream end of the second graft is correctly placed in the downstream neck of the aneurysm being treated. This can lead to a greater overlap than is the minimum required but is a useful technique to ensure that the overall length of the graft is correct.
It is sometimes the case that the aneurysm extends up to or slightly beyond an arterial bifurcation. In such a case it is possible to place a graft according to the present invention which has a bifurcation at its downstream end, a so-called xe2x80x9ctrouser graftxe2x80x9d, wholly within the primary artery. A supplemental graft may then be introduced through each of the subsidiary arteries and overlapped with the respective lumenae of the bifurcated part of the primary graft. In the case of an aneurysm in the aorta, for instance, that extended into each of the iliac arteries the primary graft of the xe2x80x9ctrousersxe2x80x9d type would be placed in the aorta through one of the iliac arteries. Supplemental grafts which dock with the bifurcated end of the primary graft would then be inserted through each of the iliac arteries.
In those cases where one graft according to this invention is to be inserted into the downstream end of another such graft it may be desirable to provide means to stop the xe2x80x9cskirtxe2x80x9d on the downstream end of the other graft from being distorted by the insertion of the one graft. This may conveniently be done in one or other of two ways. The skirt may be provided with a small number of linear reinforcement wires extending longitudinally of the graft. In this case, the wires are spaced about the circumference of the skirt. Alternatively, the skirt may be provided with at least one resilient annular reinforcement wire. The resilient reinforcement wire will spring into an expanded condition upon being released from the catheter through which it is introduced into the body. This latter arrangement is particularly suitable in the case of xe2x80x9ctrouser graftsxe2x80x9d wherein one leg of the graft will have a skirt which cannot be expanded by a balloon catheter.